Process for the production of thiophosgene

ABSTRACT

Process of producing thiophosgene by reduction of trichloromethanesulfenyl chloride with hydrogen sulfide on silica gel at 120*-180*C., preferably 130*-160* C.

United States Patent 1 3,699,161 Magerlein et al. 5] Oct. 17, 1972PROCESS FOR THE PRODUCTION OF v THIOPHOSGENE [56] References Cited [72]Inventors: Helmut Magerlein, Erlenbach; Ger- UNITED STATES PATENTS hardMeyer, Obernburg; Hans- Dieter Rupp, Erlenb h, ll f G 3,150,176 9/1964Foley ..260/543 R many Primary Examiner-Lorraine A. Weinberger [73]Asslgnee. Glanzsoff AG, Wuppertal, Germany Assistant Examiner mchardKelly [22] Filed: April 15, 1971 AttorneyJohnston, Root, OKeeffe, Keil,Thompson 21 Appl. No.1 134,495 Shmleff [57] I ABSTRACT 30 F'Al't'P"tDt 1orelgn pplca Ion "on a a Process of producing thiophosgene by reductionof p 17, 1970 Germany 20 18 381-7 trichloro methanesulfenyl chloridewith hydrogen sultide on silica gel at l20l80C., preferably l30l 60 [52]U.S.Cl. ..260/543R [51] Int. Cl ..C07c 51/58 [58] Field of Search..260/543 R 10 Claims, No Drawings PROCESS FOR THE PRODUCTION OF BO ENEThiophosgene is a valuable initial reactant for the synthesis ofnumerous organic sulfur compounds, such 5 as thioureas, isothiocyanates,dithiocarbamates, thiocarbonates, chlorothioformates and the like. 3

1n the earliest known processes, thiophosgene was prepared by reactingtrichloromethanesulfenyl chloride with silver dust, tin and hydrochloricacid, tin

only 50 to 60 percent. Another process is known in whichtrichloromethanesulfenyl chloride is reacted at elevated temperatureswith hydrocarbons which either readily give off hydrogen or in whichatleast part of the hydrogen is easily replaced by chlorine atoms (GermanPat. No. 853,162). In this process, the best results are obtained byusing tetralin as the hydrocarbon. The process is uneconomical onaccount of the high cost of theparticular hydrocarbons required.Moreover, this process has the disadvantage that the decomposition andside reactions of trichloromethanesulfenyl chloride are favored by thenecessarily high reaction temperatures so that yields of only about 80percent can be obtained.

According to a similar process, it is known that,

trichloromethylsulfenyl chloride can be reacted in the presence ofFriedel-Crafts catalysts at temperatures of 75C. to 250C. with anaromatic hydrocarbon having hydrogen atoms which are easily substitutedby chlorine atoms (U.S. Pat. No. 2,668,853). The hydrocarbons used forthis process are benzene or its homologs or derivatives, e.g. xylenes orchlorobenzenes. This process is uneconomical because the resultingmixtures of chlorinated hydrocarbons are difficult toutilize, andmoreover the yields are again only about 80 percent of theory.

It is also known that trichloromethanesulfenyl chloride can be reducedwith hydrogen (German Pat. No. 873,836). In this process,trichloromethanesulfenyl chloride and excess hydrogen are introducedinto a reaction tube, which may contain inert fillers or catalystcarriers, at temperatures of 300C. to 400C. This process is onlyworthwhile if it is carried out as a cyclic continuous process, but eventhen this procedure is complicated and costly due to the additionalseparating processes required for recovering the unreacted components.Moreover, at the reaction temperatures employed, considerable quantitiesof trichloromethanesulfenyl chloride are decomposed by heat into carbontetrachloride and sulfur.

on an industrial scale by these processesbecause of the high cost ofdiethylphosphiteand of white phosphorus.

It is also known to use sulfur dioxide as a reducing agent for thepreparation of thiophosgene from trichloromethanesulfenyl chloride(French Pat. No. 1,152,827). The yields obtained by this process areonly 50 to. percent.

Thiophosgene can be prepared by a more recently developed processinvolving the reaction of trichloromethanes'ulfenyl chloride with sulfurdioxide or hydrogen sulfide in the presence of a two phase system ofwater/organic solvent and with iodide ions as the catalyst (Czech PatentNo. 103,963). Thiophosgene can be produced on a large industrial scaleby this process if sulfur dioxide is used as reducing agent because theyield in this case is 92 percent of the theory. The reaction takes placein accordancewith the following overall reaction equation:

The aqueous phasev containing sulfuric acid. hydrochloric acidasby-products must be discarded because it would be uneconomical toseparate and recover the acids. The recovery of thiophosgene from theorganic phase requires an expensive distillation process. If hydrogensulfide wereto be used as reducing agent in this process, the yieldobtained would be only percent of theory.

Hydrogen sulfide accumulates in considerable quantities in the chemicalindustry, e.g. from the production of carbon disulfide, and is readilyavailable as an inexpensive reducing agent. It has therefore been ofconsiderable interest to discover a process by whichtrichloromethanesulfenyl chloride could be reduced to thiophosgene inhigh yields by using hydrogen sulfide as the reducing agent.

Accordingly, it is the primary object of the invention to provide aneconomical and effective commercial process for producing thiophosgenefrom trichloromethanesulfenyl chloride and hydrogen sulfide. Accordingto the invention, this object is achieved so as to produce thiophosgenein high yields by carrying out the reduction of trichloromethanesulfenylchloride with hydrogen sulfide at temperatures in the range ofapproximately C. to C. and in contact with silica gel.

When trichloromethanesulfenyl chloride is treated with hydrogen sulfideat elevated temperatures, it reacts primarily in accordance withEquation 2 to form thiophosgene:

The other products of the reaction are hydrogen chloride and sulfur. Inaddition to this main reaction, two side reactions take place Two otherprocesses for the preparation 0 (trichloromethyl)-trisulfide is formedin accordance thiophosgene are known which involve the reaction ofthiochloromethane-sulfenyl chloride, either with diethylphosphite (USSRPat. No. 105,336) or with white phosphorus (U.S. Pat. No. 3,150,176).Althoughthe yields in these processes are 85 percent of the theory and91 percent of the theory, respectively, and therefore higher than in theother processes described above, thiophosgene cannot be economicallyprepared with the Equation 3 and carbon disulfide in accordance withEquation 4.

Cl CSC1+ 2 H s CS,+ 4 HC1+ S 4 r The reaction oftrichloromethanesulfenyl chloride with hydrogen sulfide takes placeextremely rapidly in contact with silica gel so that this reaction canunexinv which bis-' The reaction of the invention is advantageouslycarried out at temperatures in the range of about 130C. to 160C. becauseno bis-(trichloromethyl) trisulfide is formed under theseconditions. Theformation of carbon disulfide according to Equation 4 is also largelysuppressed at this temperature range so that thiophosgene isobtained invery high yields. It is only above 160C. that carbon disulfide isincreasingly formed asa by-product in accordance with Equation 4.

1n the process according to the invention, trichloromethanesulfenylchloride and hydrogen sulfide are advantageously used in equivalentquantities, i.e. in stoichiometric proportions of 1:1 in accordance withEquation v2. An excess of hydrogen sulfide favors the formation ofcarbon disulfide whereas an excess of trichloromethanesulfenyl chlorideis uneconomical because the unreacted portion must be separated andreturned to the reaction.

Ordinary commercially available types of silica gel are used for theprocess of the invention, preferably a xerogel or even an. aerogel inthe form of relatively large agglomerate particles. Silica gels having aparticle size range of 1.5 to 3 mm. (agglomerate particles) and a bulkdensity, i.e. the apparent density or so-called 4 preferred and mostadvantageous ranges of the physical properties of the catalytic silicagel of the invention:

TABLE Range Property Broad Narrow Particle size,

agglomerate (mm) 0.2-8 1.5-3.0 Bulk density (g/cc.) 0.1-0.9 0.6 v .9Ultimate particles size 1- 000 3-30 (millimicrons) Packing density(glcc.) 0.18-0.6 0.3-0.5 Specific surface area (mlg) 100-800 300-700Micropore volume (cc./g) 0.3-2.0 0.4-0.9 Average pore diameter It willbe recognized that the invention is not dependent upon the selection ofa specific silica gelother than when achieving the most advantageousresults within thenarrow ranges given in the precedingtable.

The reaction mixture obtained from the process according to theinvention consists essentially of liquid sulfur and a gaseous mixture ofthiophosgene,

hydrogen chloride and small quantities of carbon disulgel density, of0.6 to 0.9 g/cc. have been found to be especially suitable. The silicagel is preferably dried at 120C. to 150C. before use.

The preparation of a silica gel having a reasonably rigid agglomeratestructure andv particle size sufficient to form a fixed catalytic bedcan be carried out by known methods, and there is a wide range ofselection of suitable silica gels in the commercial market. A xerogel'isa silica gel from which the liquidphase has been evaporated so as toform a more or less hard agglomerate of ultimate silica particles. Theparticle size referred to above as being especially preferred is theparticle size of the agglomerate and not the primary or ultimateparticlesize which may be on the order of 3 to 30 millimicrons. Ingeneral, these ultimate particle sizes can range from as low as l-20millimicrons to more than 1,000 millimicrons. Also, it should be notedthat the bulk or apparent density of the agglomerate particles of silicagel is the weight per unit volume in the fixed bed, as distinguishedfrom the so-called packing density" as defined by E. Manegold,Kolloid-Z.,'Vol. 96 page 186 1941 under the formula S= 0.455/( Vp+0.455)

wherein S is the packing density and Vp is the microporevolume in cc.per gram.

in general, it is desirable to employ a silica gel of relatively highsurface area per unit weight, consistent with a stable catalyst bed.However, this value of specific surface area can be varied within widelimits, usually in a range of at least 100 m lg or approximately 200 to800 m /g. Even relatively dense silica gel powders with a rather lowspecific surface area can be employed. The following table thereforesummarizes the fide. The gas mixture can be worked up in a conventionalmanner, e.g. by fractional condensation. A very pure thiophosgene iseasily obtained in this method of separation and recovery of gaseousproducts.

The process according to the invention may be carried out eithercontinuously or intermittently by various methods. The reaction ispreferably carried out continuously in'a reactiontube or elongatedtubular reaction zone which is filled with the particles of silica gelas a fixed bed and into which trichloromethanesulfenyl chloride andhydrogen sulfide are introduced, a temperature of C. to. C. preferablybeing maintained in the reaction zone.

It has been found that the best results are obtained when the reactantsare passed through the reaction tube in the same direction, i.e. withcocurrent flow of both reactants. The stoichiometric amounts oftrichloromethanesulfenyl chloride and hydrogen sulfide are mostadvantageously both introduced into the top of a reaction tube whichisfilled with the silica gel while the gaseous mixture of thiophosgene,carbon disulfide and hydrogen chloride and the liquid sulfur are removedfrom the lower end of the reaction tube.

The yield obtained in the process according to the invention is 94percent of theory. In none of the previously known processes canthiophosgene be obtained consistently in such high yields.

The process according to the invention is further distinguished frommost of the known processes in being very economical since hydrogensulfide, which is much less expensive, is used as the reactant for partof the catalyst is lost by reaction with the impurities in the reactionmixture and must therefore be replaced. The quantity of catalystrequired therefore depends on the purity of the starting material and ofthe solvent used and must therefore be determined analytically. 1n theprocess according to the invention, on the other hand, no solvent isrequired. The silica gel catalyst is not used up in the reaction anddoes not lose its activity even after prolonged use.

The process is more fully illustrated by the following example.

EXAMPLE A double-walled glass reaction tube having a length of 1 meterand an internal diameter of 15 mm. is filled with 120 grams of silicagel (particle size 1.5 to 3 mm., bulk density 0.7 grams/cc.) was used.The tube was heated to and maintained at a temperature of 135C., Icontrolled by means of a circulation thermostat.

17.75 grams/hour (95 m mol/hr) of trichloromethanesulfenyl chloride and3.25 grams/hour (95 m mol/hr) of hydrogen sulfide were continuouslyintroduced through two feed pipes at the head of the reaction tube bymeans of a dosing pump. The liquid sulfur formed was collected in aflask heated to 135C. at the lower end of thereaction tube and was notcontaminated with trichloromethanesulfenyl chloride. The gaseousreaction products were also removed at the lower end of the reactiontube. The gases in the product were condensed in a condenser andcollected in a wash bottle which was filled with half concentratedhydrochloric acid and cooled to C.

After an initial period of 5 hours, constant conditions had becomeestablished in the reaction tube. The organic phase forming in the washbottle was then removed at the rate of 10.75 grams/hour. It consisted of96 percent by weight of thiophosgene and 4 percent by weight of carbondisulfide and was free from trichloromethanesulfenyl chloride. Theoverall conversion was therefore quantitative and the yield ofthiophosgene was 94 percent of the theory.

In an alternative procedure the gaseous mixture v withdrawn at the lowerend of the reaction tube is fractionally condensed after achievingconstant conditions in the reaction, thereby separating approximatelythe same amount of thiophosgene as the main product. The l-lCl can bereadily absorbed in water to complete the separation of gases. Nospecial solvents or recycle streams are required, and the silica gelcatalyst exhibits a very long life. The number and amount of byproductsis quite limited.

The invention is hereby claimed as follows:

1. A process for the production of thiophosgene which comprises reducingtrichloromethanesulfenyl chloride by reaction with hydrogen sulfide at atemperature between about C. and 180C. and in contact with silica gel.

2. A process as claimed in claim 1 wherein the reaction is carried outat a temperature of about C. to C.

3. A process as claimed in claim 1 wherein said trichloromethanesulfenylchloride and hydrogen sulfide are reacted in approximatelystoichiometric amounts. h

4. A process as claimed in claim 1 wherein said silica gel has aparticle size of about l.5 to 3.0 mm. and a bulk density in the range ofapproximately 0.6 to 0.9 g/cm.

I 5. A process as claimed in claim 1 carried out continuously by passingsaid trichloromethanesulfenyl chloride and hydrogen sulfide cocurrentlythrough a fixed bed of silica gel in-an elongated tubular reaction zonemaintained at said temperature of between about 120C. and C.

6. A process as claimed in claim 5 wherein said trichloromethanesulfenylchloride and hydrogen sulfide are continuously introduced into saidreaction zone in approximately stoichiometric amounts.

7. A process as claimed in claim 6 wherein the temperature in saidreaction zone is about 130C. to 160C.

10. A process as claimed in claim 8 wherein the reaction productsremoved at the lower end of the reaction tube include liquid sulfur anda gaseous mixture of thiophosgene, carbon disultide and hydrogenchloride, the gases being separated from the liquid sulfur and thenfractionally condensed to separate and recover said thiophosgene.

2. A process as claimed in claim 1 wherein the reaction is carried outat a temperature of about 130*C. to 160*C.
 3. A process as claimed inclaim 1 wherein said trichloromethanesulfenyl chloride and hydrogensulfide are reacted in approximately stoichiometric amounts.
 4. Aprocess as claimed in claim 1 wherein said silica gel has a particlesize of about 1.5 to 3.0 mm. and a bulk density in the range ofapproximately 0.6 to 0.9 g/cm3.
 5. A process as claimed in claim 1carried out continuously by passing said trichloromethanesulfenylchloride and hydrogen sulfide cocurrently through a fixed bed of silicagel in an elongated tubular reaction zone maintained at said temperatureof between about 120*C. and 180*C.
 6. A process as claimed in claim 5wherein said trichloromethanesulfenyl chloride and hydrogen sulfide arecontinuously introduced into said reaction zone in approximatelystoichiometric amounts.
 7. A process as claimed in claim 6 wherein thetemperature in said reaction zone is about 130*C. to 160*C.
 8. A processas claimed in claim 5 wherein the reactants are introduced into the topof a vertically positioned reaction tube packed with said silica gel andthe reaction products are removed at the lower end of the reaction tube.9. A process as claimed in claim 8 wherein said silica gel has aparticle size of about 1.5 to 3.0 mm. and a bulk density in the range ofapproximately 0.6 to 0.9 g/cm3.
 10. A process as claimed in claim 8wherein the reaction products removed at the lower end of the reactiontube include liquid sulfur and a gaseous mixture of thiophosgene, carbondisulfide and hydrogen chloride, the gases being separated from theliquid sulfur and then fractionally condensed to separate and recoversaid thiophosgene.